YAML Validator

Validate, format, and visualize YAML data

Common YAML Errors & How to Fix Them

Learn about common YAML validation errors and how to fix them.

Error TypeDescription & SolutionCode Example

Tabs Used for Indentation

YAML strictly forbids tabs for indentation. You must use spaces (usually 2).

Common causes:
  • Editor configured to insert tabs
  • Copy-pasting from other files
  • Habit from other languages
How to fix:
  1. Replace all tabs with spaces
  2. Default to 2 spaces for standard YAML indentation
  3. Configure your editor to "Insert Spaces" when pressing Tab
Incorrect
Correct

Missing Space After Colon

In YAML, a colon for a key:value pair must be followed by at least one space.

Common causes:
  • Typing fast
  • JSON habits (JSON allows "key":value)
  • Compact formatting attempts
How to fix:
  1. Add a space after every colon that acts as a key-value separator
  2. Ensure lists look like "- item", not "-item"
Incorrect
Correct

Inconsistent Indentation

Child elements must be indented relative to their parent. All sibling elements must share the exact same indentation level.

Common causes:
  • Mixing 2 spaces and 4 spaces
  • Visual misalignment
  • Copy-pasting blocks with different indentation
How to fix:
  1. Align all sibling keys exactly vertically
  2. Ensure children are indented (e.g., 2 spaces) deeper than the parent
Incorrect
Correct

Duplicate Keys

A mapping cannot contain duplicate keys. The behavior is undefined and parsers will often error or overwrite the first value.

Common causes:
  • Merging two config blocks
  • Copy-paste errors
  • Long configuration files
How to fix:
  1. Key names within the same object level must be unique
  2. Remove or rename one of the duplicate keys
Incorrect
Correct

Unquoted Special Characters

Strings containing special characters like :, {, }, [, ], ,, &, *, #, ?, |, - must often be quoted.

Common causes:
  • Using special chars in passwords or commands
  • Starting a value with a special character
How to fix:
  1. Wrap values containing special symbols in quotes
  2. Use single quotes (') to treat the content literally
  3. Use double quotes (") if you need escape sequences
Incorrect
Correct

Missing Dash in List

Array items must be prefixed with a dash (-) and a space. Missing the dash makes it a key-value pair or invalid syntax.

Common causes:
  • Forgetting list syntax
  • Trying to make a list look like plain text
How to fix:
  1. Add a dash and space (- ) before each list item
  2. Or use the inline format: [Apple, Banana, Orange]
Incorrect
Correct

Related Resources

JSON to YAML Converter

Convert your JSON data to YAML format instantly.

YAML Validator — YAML Validator & Linter (v1.0.0)

A powerful YAML validator and formatter used to check syntax, structure, and indentation. This tool helps you validate, format, and analyze YAML files instantly. It is ideal for developers working with Kubernetes, Docker Compose, Ansible, API configurations, and any system that uses human-friendly YAML structures.

Features

  • Validate YAML syntax instantly
  • Beautify and auto-format YAML
  • Show error messages with line numbers
  • Support for nested structures and complex YAML
  • Highlight incorrect indentation or invalid characters

Why YAML Validation Matters

  • Prevents configuration errors before deployment
  • Ensures YAML consistency across projects
  • Boosts reliability for DevOps and microservices
  • Avoids Kubernetes and CI/CD pipeline failures

Example YAML


# Sample YAML file
name: "John Doe"
age: 30
hobbies:
  - "Reading"
  - "Traveling"
  - "Gardening"

How to Validate YAML

  1. Enter or paste your YAML into the editor.
  2. Click 'Validate YAML' to analyze the structure.
  3. Fix highlighted errors shown with line numbers.
  4. Use 'Format YAML' to beautify and clean the code.

Helpful Resources

What Is a YAML File?

YAML (YAML Ain’t Markup Language) is a human-friendly data serialization format widely used for configuration files and structured data. Unlike JSON, YAML uses indentation to show hierarchy, making it easier for humans to read and write. YAML supports lists, objects, nested structures, and multi-document formats, making it ideal for DevOps and backend workflows.

What Is the YAML Validator Editor?

The YAML Validator Editor lets you write, paste, and validate YAML instantly. With real-time syntax highlighting, intelligent error detection, and clean formatting, it helps ensure your YAML configuration files are correct before deployment — essential for Kubernetes, CI/CD pipelines, and API configuration.

How the YAML Validator Works

When you enter YAML in the editor, our parser checks for syntax issues, incorrect indentation, invalid structures, and formatting problems. Clicking Validate YAML triggers a detailed analysis. Errors are highlighted, with line numbers and clear messages to help you fix issues quickly. If your YAML is valid, the tool confirms successful validation.

Why Use the YAML Validator?

Whether you manage application settings, infrastructure templates, automation scripts, or API definitions, this validator ensures your YAML files are error-free and ready for production. It helps you avoid misconfigurations, improves code quality, and ensures smoother deployments across DevOps and cloud platforms.